An encapsulant is usually used in light emitting materials, for example LEDs for encasing the light emitting elements, for example a diode which connects with chips. During the operation of manufacturing LEDs, especially dry reflow, a rapid rise in temperature occurs, subjecting the encapsulant to thermal shock. In addition, when the LED is turned on and off repeatedly, the encapsulant is exposed to temperature cycles. In addition to normal use, LEDs are also exposed to environmental changes in temperature and humidity, as well as subject to physical shocks. Therefore, optimal performance of the encapsulant for LEDs is required.
Previously, epoxy resins were used as encapsulant for LEDs since they show good mechanical properties. However, epoxy resins easily show yellowing under UV/thermal condition. Silicone materials were further developed for replacing epoxy resins as the encapsulant in LEDs.
For example, JP 2005068268 A discloses a curable composition for optical materials, comprising:                an organopolysiloxane having an alkenyl group and a phenyl group;        an isocyanurate compound having an alkenyl group;        an organohydrogensiloxane having at least four SiH bonds in one molecule;        an organosiloxane having a phenyl group and two or three SiH bonds in one molecule; and        a hydrosilylation catalyst.        
JP 2010100758 A disclose a silicone composition comprising:                (A) a compound having two or more Si—H groups in the molecule;        (B) a prepolymer having two or more carbon-carbon double bonds; and        (C) a hydrosilylation catalyst.        
JP 2009270101 A discloses a silicone composition comprising:                (A) a polyorganosiloxane having more than two alkenyl groups;        (B) a polyorganohydrogensiloxane containing reaction product of organosiloxane oligomer having more than two SiH groups with isocyanurate having at least one alkenyl group,        (C) hydrosilylation catalyst and/or radical initiator.        
In addition, WO 2011007789 A discloses a silicone composition comprising:                (A) an organic compound having a number-average molecular weight of 10,000 or lower and having, per molecule, at least two carbon-carbon double bonds reactive with an SiH group,        (B) a polysiloxane compound which contains at least two SiH groups per molecule,        (C) a hydrosilylation catalyst, and        (D) a silicone compound which has a structure represented by the general formula R1nSiO(4-n)/2.        
Silicone compositions generally show better heat stability and light stability than those of epoxy resins. However, the mechanical properties of silicone materials are usually weak and thus these materials tend to crack and delaminate when used as the encapsulant in LED devices, such as LED cups.
There is a need for silicone materials, which have both, good thermal resistance and good mechanical properties for LED application.